Submersible vehicles are presently used for a wide variety of underwater operations, including inspection of telephone lines and pipe lines, exploration for natural resources, performance of bio-mass surveys of marine life, inspection of hulls of surface vessels or other underwater structures, and to search for shipwrecks and sunken relics. Submersible vehicles may be manned or unmanned, and may carry a wide variety of payloads. Furthermore, submersible vehicles may be towed by a surface vessel, or may be equipped with a propulsion unit for autonomous mobility. Overall, submersible vehicles are an important tool in the performance of a wide variety of hydrographic surveys for commercial, ecological, professional, or recreational purposes.
FIG. 1 shows a towed submersible vehicle 10 and related support equipment in accordance with the prior art. In this embodiment, the submersible vehicle 10 includes a hull 12 having a streamlined cylindrical body 13. Several fins 14 project radially from the hull 12 as fixed control surfaces. The front (or bow) of the body 13 includes an open aperture 16 covered by a transparent window 18. The body 13 has a substantially enclosed back (or stem) 20 and a tail section 22 which is attached to the back 20 and which has a vertical steering flap 24 and a horizontal steering flap 26. The vertical and horizontal steering flaps 24, 26 are actuated by a pair of actuators (not shown) which are disposed within a payload area 21 inside the body 13. Actuator arms 28 extend through the back 20 of the hull 12 to actuate the vertical and horizontal steering flaps 24, 26.
The hull 12 also includes a tow point 30 located on an upper portion of the body 13 for attaching the submersible vehicle 10 to a tether or tow cable of a surface vessel. A pair of runners 32 are attached to the lower fins 14 to protect the vehicle from striking rocks or other objects on the ocean floor.
Support equipment for the submersible vehicle 10 includes a control unit 34, which is connected to the submersible vehicle 10 by an umbilical 36. Power is delivered to the submersible vehicle 10 through the umbilical 36, and control signals from the controller 34 are transmitted through the umbilical 36 to the actuators for independently actuating the vertical steering flap 24 and the horizontal steering flap 26. In the embodiment shown in FIG. 1, a viewing visor 38 may be connected by the umbilical 36 to a camera located within the payload compartment 21 which transmits photographic images of the underwater scene to the viewing visor 38. A camera control box 40 is electronically coupled to the camera by the umbilical 36, enabling an operator on the surface vessel to adjust the photographic images as desired.
In operation, the submersible vehicle 10 is towed behind a surface vessel over an area of interest, such as a pipeline, potential fishing area, or potential shipwreck area. Wearing the viewing visor 38, the operator uses the controller 34 to control the movement of the submersible vehicle by adjusting the deflections of the vertical and horizontal steering flaps 24, 26. Lateral movement of the submersible vehicle 10 is controlled by deflecting the vertical steering flap 24, causing the vehicle to turn to the right or left (i.e. "yaw"). The depth of the submersible vehicle 10 is controlled by deflecting the horizontal steering flap 26, causing the bow of the vehicle to pitch up or down (i.e. "pitch"). In this way, the operator is able to control the flight of the submersible vehicle 10 over the areas of interest on the ocean floor to perform inspections or acquire desired information.
Although desirable results have been achieved using the prior art system, several characteristics of the submersible vehicle 10 leave room for improvement. For instance, when the vehicle 10 is being towed in a current, especially a current that flows across the direction of travel of the surface vessel, the submersible vehicle 10 may become unstable. Cross-currents tend to cause the submersible vehicle 10 to "roll" about a lengthwise axis so that the runners 32 may no longer remain below the vehicle for protection. The rolling of the submersible vehicle 10 may also interfere with or disable the data acquisition equipment contained within the payload section. Strong currents along the direction of travel of the surface vessel (i.e. along the freestream flow direction) may also hamper the controllability of the vehicle 10.
Also, undesirable rolling characteristics are experienced when the submersible vehicle 10 is guided by the operator to a position that is laterally displaced to the sides of the surface vessel. That is, when the submersible vehicle 10 is flown out widely to the left or to the right of the surface vessel, the tether which is attached to the tow point 30 pulls on the tow point causing the vehicle to roll undesirably.
Furthermore, under some operating conditions, the shape and orientation of the fins 14 and the vertical and horizontal steering flaps 24, 26 fail to provide the desired hydrodynamic stability and controllability of the submersible vehicle 10. In rough seas and high currents, such as those which may be experienced in the fisheries of the North Atlantic and North Pacific Oceans, and in some areas commonly associated with shipwrecks in the southeastern Pacific Ocean, prior art submersible vehicles sometimes fail to provide adequate or required stability or maneuverability characteristics, including roll, pitch, and yaw control.